01 - Preheat oven to 350°F. Line a 12-cup muffin tin with paper liners.
02 - In a large mixing bowl, whisk together all-purpose flour, unsweetened cocoa powder, granulated sugar, baking powder, baking soda, and salt until thoroughly blended.
03 - In a separate bowl, whisk eggs, whole milk, vegetable oil, peppermint extract, and vanilla extract until mixture is homogenous.
04 - Pour wet ingredients into the dry ingredients and mix gently with a spatula until just incorporated. Do not overmix.
05 - Gently fold in chocolate chips, mini marshmallows, and crushed peppermint candies until evenly distributed throughout the batter.
06 - Divide batter evenly among muffin cups, filling each about three-quarters full. Sprinkle extra chocolate chips, marshmallows, and peppermint candies on top for garnish.
07 - Bake in the preheated oven for 18 to 20 minutes, or until a toothpick inserted into the center of a muffin emerges with a few moist crumbs.
08 - Allow muffins to cool in the baking tin for 5 minutes, then carefully transfer them to a wire rack to cool completely.